Laser-guided munitions (generally referred to as laser-guided bombs (LGBs), laser guided weapon systems (such as in an aircraft), or laser-guided weapons (LGWs) use a laser designator to mark (illuminate, “paint”) a target. The reflected laser light (“sparkle”) from the target is then detected by the seeker head of the weapon, which sends signals to the weapon's control surfaces (e.g., fins) to guide the weapon toward the designated point. The illuminating laser light is encoded, and the laser receiver in the LGW is set to react only to reflected laser light having the proper code.
FIG. 1 illustrates an exemplary procedure for aircraft with laser-guided weapons (LGWs) and laser spot trackers, as set forth in Joint Pub 3-09.1, Joint Tactics, Techniques, and Procedures for Laser Designation Operations, 28 May 1999, incorporated in its entirety by reference herein, at page B-B-2.
In this scenario 100, an aircraft 102 is equipped with a LGW 104 which is shown already in its ballistic trajectory towards a target 106. Also illustrated is a forward air controller (FAC) 108, and a laser designator operator (LDO) 110. The FAC 108 is in radio communication with the pilot of the aircraft 102 and with the LDO 110. The LDO 110 illuminates the target 106 with a laser, and laser light is reflected back, typically as scattered reflections called “sparkle”.
Generally, the sequence of events is that the maneuver unit commander (not shown) decides to request close air support. The FAC coordinates laser code, laser target line and frequency and/or call sign of the LDO. The airstrike request includes laser-related data. An airstrike approval message is received, and the aircraft is dispatched to a contact point to check in with FAC. The FAC coordinates laser code, laser-target line and frequency and/or call sign with LDO and pilot. Approaching the target, the aircraft calls in. The FAC relays laser control calls. The LDO designates the target (by illuminating it with laser beam). The aircraft acquires the target or releases the LGW. The LGW heads towards the target, adjusting its trajectory based on sparkle from the laser-illuminated target. The target is destroyed.
In the prior art, many techniques have been devised to improve the accuracy of the identification of the target by the seeker head of LGWs.
For example, co-owned U.S. Pat. No. 8,451,432 describes, inter alia, a method of reducing errors due to beam irregularities or hot spots, which reduce the stability and accuracy of the centroid of the spot on the quadrant detector. Existing approaches use diffusers, fiber optic faceplates, or lenslets to create a pattern on the detector to improve spatial homogenization. U.S. Pat. No. 7,498,558 uses a non-imaging lens to distort the wave front. U.S. Pat. No. 7,575,191 is similar to the above, except that it specifies a purchased engineering diffuser rather than describe the manufacturing process. U.S. Pat. No. 8,164,037 describes a dual-mode semi active laser (SAL) with a spreader element that is wide in its definition. U.S. Pat. No. 8,188,411 describes an integrated stack, including a spreader element comprising an array of lenslets, typically rectangular, or a diffuser. U.S. Pat. No. 8,207,481 describes the use of a Fresnel lens. This is a single focus system that uses the Fresnel lens to reduce size and weight.